Keepers for MRAM electrodes

ABSTRACT

A magnetic memory device, preferably a magnetic random access memory (MRAM) and method for forming same are described wherein a bit region sensitive to magnetic fields and preferably comprising a tunneling magnetoresistance (TMR) structure is located between a top electrode with a magnetic keeper and a bottom electrode with a magnetic keeper. The top electrode is preferably made of copper using a damascene process. The magnetic keeper of the top electrode includes at least a magnetic laterial layer (e.g., Co—Fe) but in the illustrated embodiments also includes one or more barrier layer (e.g., Ta). Various embodiments describe structures wherein the magnetic keeper stack is in contact with one, two or three surfaces of the top electrode, which face outward from the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed generally to magnetic memory devices forstoring digital information and, more particularly, to methods andstructures for confining magnetic fields produced by these devices.

2. Description of the Related Art

The digital memory most commonly used in computers and computer systemcomponents is the dynamic random access memory (DRAM), wherein voltagestored in capacitors represents digital bits of information. Electricpower must be supplied to these memories to maintain the informationbecause, without frequent refresh cycles, the stored charge in thecapacitors dissipates, and the information is lost. Memories thatrequire constant power are known as volatile memories.

Non-volatile memories do not need refresh cycles to preserve theirstored information, so they consume less power than volatile memories.There are many applications where non-volatile memories are preferred orrequired, such as in cell phones or in control systems of automobiles.

Magnetic random access memories (MRAMs) are non-volatile memories.Digital bits of information are stored as alternative directions ofmagnetization in a magnetic storage element or cell. The storageelements may be simple, thin ferromagnetic films or more complex layeredmagnetic thin-film structures, such as tunneling magnetoresistance (TMR)or giant magnetoresistance (GMR) elements.

Memory array structures are formed generally of a first set of parallelconductive lines covered by an insulating layer, over which lies asecond set of parallel conductive lines, perpendicular to the firstlines. Either of these sets of conductive lines can be the bit lines andthe other the word lines. In the simplest configuration the magneticstorage cells are sandwiched between the bit lines and the word lines attheir intersections. More complicated structures with transistor ordiode configurations can also be used. When current flows through a bitline or a word line, generates a magnetic field around the line. Thearrays are designed so that each conductive line supplies only part ofthe field needed to reverse the magnetization of the storage cells.Switching occurs only at those intersections where both word and bitlines are carrying current. Neither line by itself can switch a bit;only those cells addressed by both bit and word lines can be switched.

Magnetic memory arrays can be fabricated as part of integrated circuits(ICs) using thin film technology. As for any IC device, it is importantto use as little space as possible. But as packing density is increased,there are tradeoffs to be considered. When the memory cell size isreduced, the magnetic field required to write to the cell is increased,making it more difficult for the bit to be written. When the width andthickness of bit lines and word lines are reduced, there is highercurrent density, which can cause electro-migration problems in theconductors. Additionally, as conducting lines are made closer together,the possibility of cross talk between a conducting line and a celladjacent to the addressed cell is increased. If this happens repeatedly,the stored magnetic field of the adjacent cell is eroded throughmagnetic domain creep, and the information in the cell can be renderedunreadable.

In order to avoid affecting cells adjacent to the ones addressed, thefields associated with the bit and word lines must be stronglylocalized. Some schemes to localize magnetic fields arising fromconducting lines have been taught in the prior art.

In U.S. Pat. No. 5,039,655, Pisharody taught a method of magneticallyshielding conductive lines in a thin-film magnetic array memory on threesides with a superconducting film. At or near liquid nitrogentemperatures (i.e., below the superconducting transition temperature),superconducting materials exhibit the Meissner effect, in which perfectconductors cannot be permeated by an applied magnetic field. While thisis effective in preventing the magnetic flux of the conductive line fromreaching adjacent cells, its usefulness is limited to those applicationswhere very low temperatures can be maintained.

In U.S. Pat. No. 5,956,267, herein referred to as the '267 patent, Hurstet al. taught a method of localizing the magnetic flux of a bottomelectrode for a magnetoresistive memory by use of a magnetic keeper. Alayered stack comprising barrier layer/soft magnetic materiallayer/barrier layer was deposited as a partial or full lining along adamascene trench in a insulating layer. Conductive material wasdeposited over the lining to fill the trench. Excess conductive materialand lining layers that were on or extended above the insulating layerwere removed by polishing. Thus, the keeper material lined bottom andside surfaces of the bottom conductor, leaving the top surface of theconductor, facing the bit, free of the keeper material.

The process of the '267 patent aids in confining the magnetic field ofthe cell and avoiding cross-talk among bits. A need exists, however, forfurther improvements in lowering the writing current for a givenmagnetic field. By lowering the current required to write to a givencell, reliability of the cell is improved.

SUMMARY OF THE INVENTION

A magnetic memory array, preferably comprising an MRAM, with a series oftop electrodes in contact with a magnetic keeper on at least onesurface, a series of bottom electrodes and magnetic bit regions locatedtherebetween is described in accordance with the current invention. Themagnetic bit regions may comprise tunneling magnetoresistance or giantmagnetoresistance structures.

In an MRAM device, the structure of a magnetic keeper for the topconductor made by a damascene process includes stacked layers of barrierand magnetic materials, at least a portion of the layers magneticallyshielding at least one surface of the top conductor.

A method of forming a magnetic keeper for a top electrode in an MRAMdevice is also described, which includes depositing an insulating layerover a magnetic storage element, etching and then filling a damascenetrench with a conductive material, planarizing to remove the conductivematerial from over the insulating layer and then depositing a magneticmaterial over the conductive material.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures are meant to help illustrate, but not limit, the inventionand are not drawn to scale. The illustrated embodiment has bit lines atthe bottoms of the figures and has word lines at the tops of thefigures. The skilled artisan will understand that there are many otherpossible configurations for MRAM structures, which can take advantage ofthe teachings set forth in this invention.

FIG. 1A is a cross section of a partially fabricated MRAM structureshowing the bottom electrode, the bit region and the overlyinginsulating layer before the top electrode is fabricated.

FIG. 1B illustrates the partially fabricated MRAM structure of FIG. 1Aafter a damascene trench has been etched into the insulating layer.

FIG. 2 is a cross section showing the damascene trench of FIG. 1B linedwith a barrier material and filled with copper.

FIG. 3A is a cross section showing a blanket layer, comprising a stackof barrier/magnetic/barrier materials, deposited over the structure ofFIG. 2, in accordance with a first embodiment of the present invention.

FIG. 3B shows the structure of FIG. 3A after patterning and etching toleave the barrier and magnetic material stack over and slightly widerthan the line in which the top electrode is formed.

FIG. 4A illustrates the structure of FIG. 2 after the conductivematerial of the top electrode has been etched to make a recess into thetop electrode, in accordance with a second embodiment of the presentinvention.

FIG. 4B shows the structure of FIG. 4A after a blanket layer, comprisinga stack of barrier/magnetic/barrier materials, has been deposited overthe recessed top electrode.

FIG. 4C illustrates the structure of FIG. 4B after planarizing.

FIG. 5A illustrates the structure of FIG. 1B after a stack ofbarrier/magnetic/barrier materials has been deposited to line thedamascene trench, in accordance with a third embodiment of the presentinvention.

FIG. 5B shows the structure of FIG. 5A after a spacer etch has removedthe horizontal portions of the deposited stack of layers.

FIG. 5C is a cross section of the structure of FIG. 5B after a blanketconductive layer has been deposited to fill the trench.

FIG. 5D shows the structure of FIG. 5C after planarization of theconductive layer.

FIG. 6A illustrates the structure of FIG. 1B after barrier and magneticlayers have been deposited to line the damascene trench, in accordancewith a fourth embodiment of the present invention.

FIG. 6B is a cross section of a partially fabricated MRAM structure,wherein the conductive material has been selectively recessed, inaccordance with a fourth embodiment of the present invention.

FIG. 6C is a cross section showing the structure of FIG. 6B after ablanket layer, comprising a magnetic material layer and a barrier layer,has been deposited over the recessed conductive material and theinsulating layer.

FIG. 6D is a cross section showing the structure of FIG. 6C afterplanarizing to remove the barrier and magnetic materials stack from overthe insulating layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although aluminum is used commonly as a conductor in semiconductordevices, it has difficulty meeting the high electric currentrequirements of magnetic memory devices without suffering from damagedue to electromigration. Copper is more suitable for high currentapplications as it is more resistant to electromigration. Whereasaluminum lines can be fabricated by patterning with photoresist anddryetching, copper is difficult to dry etch. Copper lines are thuspreferably fabricated by a damascene process. Trenches are formed in aninsulating layer, a copper layer is deposited to overfill the trench andthe excess copper is removed by polishing down to the surface of theinsulating layer.

As discussed above, the '267 patent provides magnetic keepers for bottomelectrodes, fabricated by a damascene process. The preferred embodimentsdescribed herein provide magnetic keepers, in various configurations,for top electrodes made by a damascene process in integrated magneticmemory devices. The process of the '267 patent, however, is not suitablefor forming keepers for a top electrode.

The preferred embodiments of the invention can be understood withreference to the figures. Only individual magnetic memory structures areshown in the figures, but it will be understood that the illustratedindividual cells are representative of similar structures repeatedacross a memory array. FIGS. 1A and 1B show, in cross section, apartially fabricated MRAM cell that will be used as the starting pointfor describing the embodiments contained herein.

The memory cell comprises a bottom electrode structure 10, which, inturn, comprises a lower conducting line 12 that runs from side to sideacross the page and is made, preferably, of copper. The bottom electrode10 typically overlays a semiconductor substrate (not shown). A barrierlayer 14 preferably encapsulates the copper line on all four sides alongits length. The barrier layer 14 can comprise tantalum (Ta) or anothermaterial that blocks diffusion of copper and is compatible withintegrated circuit manufacture. In this cross-sectional view, the copperline is cut near the center along its long axis, so that only theportions of the barrier layer that clad the lower line 12 along theupper surface 18 and the lower surface 20 can be seen. The claddingalong one side of the line is above the plane of the page and along theother side of the line is below the plane of the page. In a preferredembodiment (and according to the prior art), the upper surface 18 of theline 12 is covered by only the barrier layer 14, but the lower surface20 and the two side surfaces are further clad by a sandwich structurecomprising barrier layer/soft magnetic material/barrier layer, whichserves as a magnetic keeper for the conducting line 12, in accordancewith the teachings of the '267 patent. A “magnetic keeper,” as usedherein, includes at least a magnetic material layer; in the preferredembodiments the magnetic keeper also includes one or two barrier layers.There is preferably no magnetic material on the top surface of the lowerline 12 that faces toward a magnetic memory cell or bit 24 capped with abarrier layer 28 and formed in an insulating layer 26. Magnetic materialbetween the lower line 12 and the bit 24 would interfere with themagnetic field from the lower line 12 acting upon the magnetic bit 24.

In FIGS. 1A and 1B, as well as the embodiments discussed below, thebottom electrode is formed along the lower line 12, which serves as abit line in the illustrated “cross-point” circuit configurations. Inother arrangements, the skilled artisan will readily appreciate that thebit line can be formed above the bit element and the word line below,and that the bit can also be latched to a transistor or diode.

The magnetic memory cell 24 can be any magnetic structure that storesbits of information defined by the direction or polarity ofmagnetization, including thin ferromagnetic films or more complexlayered magnetic thin-film structures, such as tunnelingmagnetoresistance (TMR) or giant magnetoresistance (GMR) elements.

The preferred magnetic memory cell is a TMR structure. The illustratedTMR structure comprises a first ferromagnetic layer 30 followed by aninsulating layer 32 and a second ferromagnetic layer 34. A well-known,exemplary TMR structure includes, within the first ferromagnetic layer30, a series of sub-layers comprising Ta/Ni—Fe/Fe—Mn/Ni—Fe. Theinsulating layer 32 of the illustrated embodiment comprises aluminumoxide, preferably in a thickness between about 0.5 nm and 2.5 nm. Thesecond ferromagnetic layer 34 preferably comprises sub-layers, Ni—Fe/Ta.As shown in FIG. 1B, the barrier layer 28 preferably overlays the secondferromagnetic layer 34.

The TMR stack can be formed by any suitable method, but is preferablyformed as a stack of blanket layers and then patterned into a pluralityof cells for the array. The insulating layer 26, preferably siliconnitride or a form of silicon oxide, is then deposited thereover andpolished back (e.g., by chemical mechanical planarization) to expose theTMR stack's top surface. Another insulating layer 36, typicallycomprising a form of silicon oxide, is deposited over the insulatinglayer 26 and the magnetic memory cell 24. Alternatively, a singleinsulating layer can take the place of the two illustrated layers 26,36.

With reference to FIG. 1B, a trench 38 is etched into the silicon oxidelayer 36 as a first step in using the damascene process to form the topelectrode, or word line, for the magnetic cell 24. The trench 38 thatwill contain the word line runs into and out of the page, perpendicularto the bottom electrode structure 10, and thus traverses several cellsin the array. In the illustration of FIG. 1B, the bottom of the trench38 is shown in contact with the barrier layer cap 28 on the top surfaceof the magnetic cell 24 as a preferred embodiment.

In another arrangement, the trench may be more shallow, leaving a thinportion of the insulating silicon oxide layer between the bottom of thetrench and the top of the magnetic cell.

An MRAM, fabricated with a top electrode 40 having no magnetic keeper,is shown in FIG. 2. The bottom electrode 10 is preferably clad with atleast a barrier layer and, more preferably, with the magnetic keeperstructure described above with reference to FIG. 1A. Using FIG. 1B as astarting point, the etched trench 38 preferably has a depth of about100-300 nm and is about 200 nm in the illustrated embodiments. The widthof trench 38 is preferably about 100-300 nm, and is about 200 nm in theillustrated embodiments. A barrier layer 42 is deposited to line thetrench 38. The preferred barrier material is tantalum, although anyconductive material that is a good diffusion barrier for confiningcopper is suitable. The thickness of the barrier layer is preferablyabout 1-20 nm, more preferably about 2-10 nm and is about 5 nm in theillustrated embodiments. A highly conductive material 44 is deposited tofill the trench 38 and form the top electrode 40 (along a word line, inthe illustrated configuration). The preferred material is copper, butother conductive materials such as aluminum, gold or silver may also beused. The copper may be deposited in a two-step process wherein first aseed layer is deposited by physical vapor deposition and then the trenchis filled completely by electroplating. Alternatively, the copper may bedeposited completely by physical vapor deposition.

In FIG. 2, the top surface 46, 48 has been planarized to remove excessbarrier and conductive material and to make the top surface 48 of thetop electrode 40 level with the top surface 46 of the insulating layer36. In the preferred embodiments, the top electrode 40 also includesmagnetic keeper structures that help confine magnetic fields within eachcell across the array. The embodiments below employ the structures ofFIG. 1B or 2 as starting points.

The embodiments that follow have magnetic keeper structures that aremulti-layered, including both barrier layers and soft magnetic materiallayers. Although this is preferred, it should be understood that thebarrier layer(s) may not be employed where the magnetic material layercan also serve as a diffusion barrier to copper, in addition toperforming the magnetic keeper function and confining the magneticfields. Thus, the term “magnetic keeper,” as used herein, includes atleast a magnetic material layer, and preferably also includes one ormore barrier layers. Alternative structures include simply a singlemagnetic material layer as the magnetic keeper or the magnetic materiallayer and only one barrier layer. The latter arrangement is shown inFIGS. 6A-6D.

Patterned Partial Keeper

The most simple configuration for a magnetic keeper for a word line isshown in the first embodiment, illustrated in FIGS. 3A and 3B. Thisembodiment can be understood using FIG. 2 as a starting point. In theillustrated embodiment, a stack 50 of blanket layers is deposited overthe planarized top surface as shown in FIG. 3A, although it is possibleto form this keeper with a magnetic material blanket layer alone. Afirst layer 52 is a barrier layer; a second layer 54 is a magneticmaterial preferably comprising a soft magnetic material, such aspermalloy (Ni—Fe) and more preferably Co—Fe, and a third layer 56 isanother barrier layer. Preferably the barrier layers comprise Ta. Thethickness of each layer in the stack is preferably about 1-20 nm, morepreferably 2-10 nm and most preferably about 5 nm. The layers in thestack 50 can be deposited by any suitable method. In the illustratedembodiment, the layers are formed by physical vapor deposition all inthe same cluster tool.

The stack 50 is patterned and etched using standard photolithographytechniques, preferably leaving a patterned partial keeper over the areadefining the memory cell. In another arrangement, the keeper ispatterned to extend along the top surface of the word line top electrode40 that runs into and out of the page as shown in the cross section ofFIG. 3B. In still another arrangement (and not shown), the blanket stackmay be patterned and etched to extend over an entire array, withopenings only over vias (not shown) in the insulating layer 36.

The overlying structure is referred to herein as a partial keeper 58because it does not overlay all external surfaces of the upper conductoror top electrode 40. “External surfaces,” as used herein, refers to allsurfaces of the top electrode 40 that do not face the magnetic storageelement or TMR stack 24 in the illustrated embodiment.

Self-Aligned Partial Keeper

FIG. 4A shows the first step in formation of a self-aligned partialkeeper from the top electrode structure of FIG. 2, in accordance with asecond embodiment. Like reference numerals are employed for elementscorresponding to those of the previous embodiment. The top surface ofthe conducting line 44 is recessed by a selective etch, preferably bywet etching. For example, a solution of glacial acetic acid and nitricacid in a 10:1 (acetic:nitric) ratio will selectively etch copper 44 ascompared to oxide 36 and tantalum 42. For other materials, the skilledartisan can readily determine a suitable selective chemistry. The depthof the recess 60 is between about 5 nm and 100 nm, more preferablybetween about 10 nm and 30 nm and most preferably about 15 nm.

Referring to FIG. 4B, a magnetic material is deposited into the recess60. In the illustrated embodiment, a stack 50 of blanket layers isdeposited over the recess 60 and top surface 46 of the insulating layer36. The illustrated stack 50 comprises a first barrier layer 52, amagnetic material layer 54 and a second barrier layer 56. Preferably thebarrier layers 52, 56 comprise Ta. The magnetic layer preferablycomprises a sQft magnetic material, such as permalloy (Ni—Fe) and morepreferably Co—Fe. The thickness of each layer in the stack is preferablyabout 1-20 nm, more preferably 2-10 nm and most preferably about 5 nm.The layers in the stack 50 can be formed in any suitable manner but arepreferably formed by physical vapor deposition all in the same clustertool.

With reference to FIG. 4C, the structure is etched back, preferablyplanarized, more preferably by chemical-mechanical polishing, whichleaves a flat top surface 62 flush with the top surface 46 of theinsulating layer 36. The planarization leaves self-aligned partialkeeper 64 within the recess 60 over the upper electrode or word line 40.

The self-aligned partial keeper 64 is referred to as such because it isconfined to the top electrode 40 without a mask step. The keeper ispartial because it covers only one out of three possible externalsurfaces of the top electrode.

Spacer Keeper

A third embodiment of the current invention is illustrated in FIGS.5A-5D. The starting point for this embodiment is the partiallyfabricated MRAM described earlier with respect to FIG. 1B, wherein thetrench 38 for the top electrode has been etched. At least a magneticmaterial layer lines the trench 38. In the illustrated embodiment, thestack 50 of layers, including the magnetic material layer 54 as well asthe barrier layers 52, 56 is deposited with good conformity over the topsurface 46 and into the trench 38 as shown in FIG. 5A. A selectivespacer etch is performed to remove the horizontal portions 66, 68, 70 ofthe stack 50. The selective etch comprises an etch with a physical(sputtering) component, such as argon ion milling or a chlorine-based orfluorine-based reactive ion etching, as will be appreciated by theskilled artisan.

FIG. 5B shows the remaining portions of the layers 52, 54, 56 along thevertical sidewalls 72 of the trench 38 after the spacer etch.Preferably, at least all the soft magnetic material layer 54 is removedfrom the bottom of the trench 38 before proceeding, as remainingmaterial can disrupt or block the interaction between the word linemagnetic field and the magnetic bit 24. While the illustrated embodimentshows all of the stack 50 removed from horizontal portions, thusensuring complete removal of the magnetic layer 54 from those portions,it will be understood that the spacer etch can also leave part of thelower barrier layer 52 over the bit 24. A spacer keeper 73 is leftlining the trench sidewalls 72.

Referring to FIG. 5C, a layer of conductive material 74, preferablycopper, is then deposited to fill the trench 38.

Referring to FIG. 5D, the conductive material 74 is planarized,preferably by chemical-mechanical polishing, which removes excessconductive material and leaves the conductive material 74 within thetrench 38 with external sidewall surfaces covered by the spacer keeper73, completing the top electrode 40 of the third embodiment.Planarization leaves an upper surface 48 flush with an upper surface 46of the insulator 36.

Self-Aligned Keeper

A self-aligned keeper, in accordance with a fourth embodiment, isdescribed with reference to FIGS. 6A-6D. This embodiment is similar tothe spacer keeper 73 as described above with respect to FIG. 5D. Thefourth embodiment uses only two layers in the magnetic keeper structure.Alternatively, the self-aligned keeper can be made with the three-layerstack described for embodiments above, or a single layer can serve asboth the magnetic layer and barrier function. The starting point forthis embodiment is the partially fabricated MRAM described earlier withrespect to FIG. 1B, wherein the trench 38 for the top electrode has beenetched.

With reference to FIG. 6A, the barrier layer 52 and the magneticmaterial layer 54 are deposited with good conformity over the topsurface 46 of the insulating layer 36 and into the trench 38. Preferablythe barrier layer 52 comprises Ta. The magnetic layer comprisespreferably a soft magnetic material, such permalloy (Ni—Fe). Co—Fe isparticularly preferred for use in this two-layer stack, whereby themagnetic material 34 will directly contact copper (see FIG. 6C). Aselective spacer etch is performed to remove the horizontal portions 76,78, 80 of the barrier layer 52 and the magnetic material layer 54. Theselective etch comprises an etch with a physical (sputtering) component,such as argon ion milling or a chlorine-based or fluorine-based reactiveion etching, as will be appreciated by the skilled artisan. Preferably,at least all the soft magnetic material layer 54 is removed from thebottom of the trench 38 before proceeding, as remaining material candisrupt or block the interaction between the word line magnetic fieldand the magnetic bit 24.

FIG. 6B shows the remaining portions of the layers 52, 54, along thevertical sidewalls 72 of the trench after the selective spacer etch, aswell as subsequent via fill and recess steps, discussed below. While theillustrated embodiment shows all material from layers 52, 54 removedfrom horizontal portions, thus ensuring complete removal of the magneticlayer 54 from those portions, it will be understood that the spacer etchcan also leave part of the barrier layer 52 over the bit 24.

As shown in other embodiments, a layer of conductive material 74,preferably copper, is deposited to fill the trench, and the top surfaceis planarized, preferably by chemical-mechanical polishing. Excessconductive material is removed, leaving conductive material 74 withinthe trench and barrier 52 and magnetic 54 layers along the externalsidewall surfaces 72. The conductive material extends along a trenchinto and out of the page, serving as an upper line 74, comprising a wordline in the illustrated arrangement.

A selective etch is performed to create a recess 82 in the top surfaceof the word line 74 as shown in FIG. 6B. The etch is performedpreferably by wet etching. For example, a solution of glacial aceticacid and nitric acid in a 10:1 (acetic:nitric) ratio will selectivelyetch the copper 74 as compared to the oxide 36. Alternatively the recess82 can be made by extending the previous chemical-mechanical polishingand using an appropriate selective chemistry with the polish. For othermaterials, the skilled artisan can readily determine a suitableselective chemistry.

With reference to FIG. 6C, at least a magnetic material and preferably asecond series of blanket layers, comprising the top portion of themagnetic keeper for this embodiment, is deposited over the top surface,filling the recess 82. Preferably, the first layer 54 is a soft magneticmaterial, such as Co—Fe, and the second layer 52 comprises a barrierlayer, such as Ta.

FIG. 6D shows the structure after chemical-mechanical polishing toremove the excess magnetic keeper material. The upper line 74 is cladalong three sides with the magnetic material layer 54 and the barrierlayer 52. Advantageously, the magnetic material is formed as acontinuous layer 54 around the three sides of the upper line 74. Theelectrode surface 84 facing the magnetic bit 24 has no magnetic materialcladding. A top surface 86 of the structure is preferably flush with theupper surface 46 of the surrounding insulating layer 36, making iteasier to perform further processing.

The self-aligned keeper 88 is referred to as such because it is confinedto the upper line 74 without a mask step. This keeper is not calledpartial because it covers all three surfaces suitable for magnetickeeper cladding.

It will be understood that the fourth embodiment, illustrated in FIGS.6A-6D, represents a combination of the second and third embodiments witha modification to two layers in the magnetic keeper structure instead ofthree. Similarly, the third embodiment can be combined with the firstembodiment, thereby also providing keeper material on three externalsurfaces of the top electrode without blocking magnetic fields betweenthe top electrode and the underlying magnetic bit. Furthermore, itshould understood that the barrier layer is not necessary to perform themagnetic keeper function and confine the magnetic fields. Alternativestructures include simply a single magnetic material layer as themagnetic keeper or the magnetic material layer one or more barrierlayers. The invention as described herein in the preferred embodimentsprovides a method for fabricating a magnetic keeper in a number ofstructures for a conducting line in a damascene trench, wherein thebottom surface of the trench has no keeper. This has particularapplication for top electrodes in magnetic memory devices. The keeperlocalizes the magnetic field surrounding the conducting line so thatonly the magnetic memory cell or bit being addressed is affected by thefield. It contains the magnetic flux and directs it toward the magneticmemory structure, thus lowering the effective current density requiredfor writing to the bit. Unaddressed neighboring bits do not feel theeffects of the magnetic field and electromigration is reduced. This aidsin compressing the design of magnetic memory arrays to smallerdimensions without sacrificing functionality.

The presently disclosed embodiments are therefore considered in allrespects to be illustrative and not restrictive. The scope of theinvention is indicated by the appended claims rather than the foregoingdescription and all changes that come within the meaning and range ofequivalence thereof are intended to be embraced therein.

I claim:
 1. A method of forming a magnetic keeper for a top electrode ina magnetic random access memory (MRAM) device, comprising: depositing aninsulating layer over a magnetic storage element; etching a damascenetrench into the insulating layer over the magnetic storage element;filling the trench with a conductive material; planarizing to remove theconductive material from over the insulating layer and to leave theconductive material within the trench; and depositing a magneticmaterial over the conductive material after planarizing.
 2. The methodof claim 1 further comprising patterning and etching the magneticmaterial so that the magnetic material covers at least a top surface ofthe conductive material.
 3. The method of claim 1 wherein the magneticmaterial extends over an array of magnetic storage elements, furthercomprising patterning and etching openings in the magnetic material overcontact vias in the insulating layer.
 4. The method of claim 1 furthercomprising, after planarizing the conductive material and beforedepositing the stacked layers, forming a recess in a top surface of theconductive layer.
 5. The method of claim 4 wherein forming the recesscomprises selectively etching the conductive material.
 6. The method ofclaim 5 wherein selectively etching comprises wet etching.
 7. The methodof claim 6 wherein wet etching comprises a solution of glacial aceticacid and nitric acid in a 10:1 (acetic:nitric) ratio.
 8. The method ofclaim 5 wherein selectively etching comprises chemical-mechanicalpolishing.
 9. The method of claim 4 further comprising, after depositingthe magnetic material, planarizing to remove the magnetic material fromover the insulating layer and to leave the magnetic material within therecess.
 10. The method of claim 1 wherein the conductive materialcomprises copper.
 11. The method of claim 10 wherein filling the trenchwith a conductive material comprises first depositing a copper seedlayer using physical vapor deposition and then electroplating copperover the seed layer.
 12. The method of claim 1 further comprisingforming an initial barrier layer as a trench lining after etching thedamascene trench and before filling the trench with conductive material.13. The method of claim 12, additionally comprising forming a magneticmaterial layer and then a top barrier layer over the initial barrierlayer as a complete trench lining.
 14. The method of claim 13, furthercomprising performing a spacer etch to remove at least all magneticmaterial from the bottom of the trench after forming the complete trenchlining and before filling the trench.
 15. The method of claim 14 whereinthe complete trench lining comprises stacked layers oftantalum/Co—Fe/tantalum.
 16. The method of claim 14 wherein the completetrench lining comprises stacked layers of tantalum/permalloy(Fe—Ni)/tantalum.
 17. The method of claim 13 wherein the complete trenchlining is formed using physical vapor deposition.
 18. The method ofclaim 13 wherein the complete trench lining is deposited in only onecluster tool.
 19. A method of forming a magnetic keeper for a topelectrode in a magnetic random access memory (MRAM), comprising:depositing an insulating layer over a magnetic storage element; etchinga damascene trench into the insulating layer over the magnetic storageelement; lining the trench with a magnetic material; selectivelyremoving the magnetic material from a bottom of the trench; and fillingthe trench with a conductive material.
 20. The method of claim 19wherein lining the trench further comprises forming a first barrierliner layer before and a second barrier liner layer after lining thetrench with the magnetic material.
 21. The method of claim 20 whereinthe first barrier liner layer is tantalum, the magnetic material isCo—Fe and the second barrier liner layer is tantalum.
 22. The method ofclaim 19 wherein selectively removing the magnetic material from thebottom of the trench comprises a selective etch with a physical etchcomponent.
 23. The method of claim 22 wherein the selective etchcomprises argon ion milling.
 24. The method of claim 22 wherein theselective etch comprises a chlorine-based or fluorine-based reactive ionetch.
 25. The method of claim 19 wherein, additionally, stacked layersof a first barrier layer, a magnetic layer and a second barrier layerare deposited onto a top surface of the conductive material.
 26. Themethod of claim 25 wherein, additionally, a recess is formed in the topsurface of the conductive material before the stacked layers aredeposited.
 27. The method of claim 26 wherein the first barrier layer istantalum, the magnetic layer is Co—Fe and the second barrier layer istantalum.
 28. The method of claim 27 wherein, additionally, a topsurface of the stacked layers is planarized.
 29. The method of claim 19wherein the magnetic storage element comprises a multi-layer tunnelingmagnetoresistance (TMR) structure.
 30. The method of claim 29 whereinthe TMR structure comprises a first ferromagnetic layer, an insulatinglayer and a second ferromagnetic layer.
 31. The method of claim 30wherein the first ferromagnetic layer includes a series of sub-layerscomprising Ta/Ni—Fe/Fe—Mn/Ni—Fe.
 32. The method of claim 30 wherein theinsulating layer comprises aluminum oxide.
 33. The method of claim 30wherein the second ferromagnetic layer comprises sub-layers Ni—Fe/Ta.34. The method of claim 19, wherein the conductive material is copper.35. The method of claim 19, wherein comprising: lining the bottom andsidewalls of the trench with a first barrier layer prior to lining thebottom and sidewalls of the trench with the magnetic material; liningthe bottom and sidewalls of the trench with a second barrier layer afterlining the bottom and sidewalls of the trench with the magneticmaterial; and prior to the filling of the trench with a conductivematerial, selectively removing the first barrier layer, the magneticmaterial, and the second barrier layer from the bottom of the trench andfrom a top surface of the insulating layer such that there issubstantially no magnetic material at the bottom of the trench and suchthat the top surface of the insulating layer is substantially flat. 36.The method of claim 19, further comprising: lining the bottom andsidewalls of the trench with a first barrier layer prior to lining thebottom and sidewalls of the trench with the magnetic material; prior tothe filling of the trench with a conductive material, selectivelyremoving the first barrier layer and the magnetic material from thebottom of the trench and from a top surface of the insulating layer suchthat there is substantially no magnetic material at the bottom of thetrench and such that the top surface of the insulating layer issubstantially flat; selectively etching a recess in a top surface of theconductive material that fills the trench such that the recess is belowa flat level of the top surface of the insulating layer; depositing asecond barrier layer on the top surface of the insulating layer and onthe recess in the top surface of the conductive material; depositing themagnetic material on the second barrier layer; and planarizing above theinsulating layer to remove the second barrier layer and the magneticmaterial from the top surface of the insulating layer.